The invention relates to a backlight module, and in particular to a lens of the backlight module for a liquid crystal display.
Several lamps make up the backlight of a direct type liquid crystal display. During manufacture, the number of tubes increases to maintain luminance in larger displays.
Referring to FIG. 1, a backlight module comprises a diffuser 11, a frame 12, a reflective sheet 13, and lamps 14. The diffuser 11 and the reflective sheet 13 are fixed by the frame 12. The lamps 14, between the diffuser 11 and the reflective sheet 13, generate light emitting directly or reflected to the diffuser 11 by the reflective sheet 13 and passing through the diffuser 11. Because luminance between the lamps 14 and reflective sheet 13 of the conventional backlight module 1 differs, the brightness of a display is not uniform. Although increasing distance d between the lamps 14 and the diffuser 11 solves the problem mentioned above, thickness of the backlight module is increased, affecting display quality.
Referring to FIG. 2, providing an additional diffuser 11a also solves problems. The thickness of the sum of the diffuser 11a and the diffuser 11 increases and the haze of the diffusers 11 and 11a blurs the outline of the lamps 14. Applying diffuser 11a not only increases the cost but also the thickness of the backlight module 1. Overlapping diffusers 11 and 11a further affects output of the light source. Increasing the number of lamps 14 to maintain luminance also increases costs.